This application is based on a patent application No. 2001-329874 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method for operating a high-pressure discharge lamp, a lighting apparatus, and a high-pressure discharge lamp apparatus.
2. Description of Related Art
Light sources generally in use for a liquid crystal projector are high-pressure discharge lamps such as high-pressure mercury lamps. As liquid crystal projectors are reduced in size and more widely used in a general household environment, it is now required to make some adjustment depending on brightness of the environment and the type of image to be projected so as to prevent the screen from being too bright. One liquid crystal projector designed to meet such requirement has a so-called dimming control function (See, for example JP 2000-131668-A). The dimming control is achieved by operating a high-pressure discharge lamp at a lower power than the rated power with the aim to adjust the brightness of lamp as well as to save power consumption.
However, the inventors of the present invention have made study on the impact of the dimming control on a conventional high-pressure discharge lamp and a conventional lighting circuit, and found a problem as follows. That is, a lighting apparatus exhibits a greater rise in the temperature in comparison with when operated at the rated power. This greater temperature rise is ascribable to excessive burden imposed on the lighting apparatus, and means that the lighting apparatus needs to be upsized and/or provided with enhanced cooling. These requirements, however, contradict a demand for a downsized, quieter projector.
An object of the present invention is to provide a method for operating a high-pressure discharge lamp, a lighting apparatus, and a high-pressure discharge lamp apparatus each capable of preventing the lighting apparatus from excessive burden even when the high-pressure discharge lamp is operated at a lower power than its rated power.
The object of the present invention stated above is achieved by a method for operating a high-pressure discharge lamp by supplying an alternating current thereto. The high-pressure discharge lamp has an arc tube in which a halogen material is sealed and a pair of electrodes is provided. The method includes: a voltage decrease detecting step of detecting that a voltage across the pair of electrodes has decreased below a predetermined level; and a low frequency current supplying step of supplying the alternating current at a lower frequency than a rated frequency for a predetermined time period. The low frequency current supplying step is performed when the voltage decrease is detected in the voltage decrease detecting step.
With this construction, even if protrusions each formed at the top of electrode grow abnormally as a result of, for example, dimming control, the protrusions are made to partly disappear so that the protrusions are reduced to a suitable size. Thus, an excessive temperature rise in the lighting apparatus is suppressed. The present invention is applicable to a DC type high-pressure discharge lamp as well as to an AC type. That is, according to the detection in the voltage decrease detection step, the direction of the direct current is reversed for a predetermined time period.
Alternatively, the object of the present invention stated above is achieved by a lighting apparatus for operating a high-pressure discharge lamp by supplying an alternative current thereto. The high-pressure discharge lamp has an arc tube in which a halogen material is sealed and a pair of electrodes is provided. The lighting apparatus includes: a voltage detector for detecting a voltage across the pair of electrodes; and a controller for controlling the alternating current so that, when the voltage detected by the voltage detector decreases below a predetermined level, the alternating current is supplied at a lower frequency than a rated frequency for a predetermined time period.
When a DC type high-pressure discharge lamp is employed, it is achieved by a lighting apparatus for operating a high-pressure discharge lamp by supplying a direct current thereto. The high-pressure discharge lamp has an arc tube in which a halogen material is sealed and a pair of electrodes is provided. The lighting apparatus includes: a voltage detector for detecting a voltage across the pair of electrodes; and a controller for controlling the direct current so that, when the voltage detected by the voltage detector decreases below a predetermined level, the direct current flows in a reversed direction for a predetermined time period.
Alternatively, the object of the present invention is achieved by a high-pressure discharge lamp apparatus including: a high-pressure discharge lamp having an arc tube in which a halogen material is sealed and a pair of electrode is provided; and a lighting apparatus for operating the high-pressure discharge lamp by supplying an alternating current thereto. The lighting apparatus includes: a voltage detector for detecting a voltage across the pair of electrodes; and a controller for controlling the alternating current so that, when the voltage detected by the voltage detector decreases below a predetermined level, the alternating current is supplied at a lower frequency than a rated frequency for a predetermined time period.
Specific examples of a high-pressure discharge lamp apparatus include various projectors, such as a liquid crystal projector, using a high-pressure discharge lamp as its light source. In addition, the examples include a general-use lighting apparatus, a headlight for a vehicle, a lighting apparatus for medical application, a curing apparatus for ultraviolet curable resin.
A high-pressure discharge lamp apparatus according to the present invention may have a socket unit for attaching a high-pressure discharge lamp but without a high-pressure discharge lamp itself (Examples of such include a projector to which a high-pressure discharge lamp is not yet attached).
Further, a high-pressure discharge lamp apparatus according to the present invention may have a high-pressure discharge lamp that is directly connected to a lighting apparatus without employing a socket unit.
When a DC type high-pressure discharge lamp is employed, the object of the present invention is achieved by the above lighting apparatus for a DC type high-pressure discharge lamp.